Two-stroke, opposed-piston internal combustion engine

ABSTRACT

In a two-stroke, opposed-piston internal combustion engine with optimized cooling and no engine block, the opposed pistons are coupled to a pair of crankshafts by connecting rods that are subject to substantially tensile forces acting between the pistons and the crankshafts.

RELATED APPLICATIONS

This is a divisional application of commonly-owned U.S. patentapplication Ser. No. 10/865,707, filed Jun. 10, 2004 for “Two-Cycle,Opposed-Piston Internal Combustion Engine,” and published asUS2005/0274332A1 on Dec. 29, 2005, now U.S. Pat. No. 7,156,056, issuedJan. 2, 2007.

The following co-pending applications, all commonly owned with thisapplication, contain subject matter related to the subject matter ofthis application:

PCT application US2005/020553, filed Jun. 10, 2005 for “Improved TwoCycle, Opposed Piston Internal Combustion Engine”, published asWO2005/124124A1 on Dec. 29, 2005;

U.S. patent application Ser. No. 11/095,250, filed Mar. 31, 2005 for“Opposed Piston, Homogeneous Charge, Pilot Ignition Engine”, publishedas US/2006/0219213 on Oct. 5, 2006, now U.S. Pat. No. 7,270,108, issuedSep. 18, 2007;

PCT application US2006/011886, filed Mar. 30, 2006 for “Opposed Piston,Homogeneous Charge, Pilot Ignition Engine”, published as WO/2006/105390on Oct. 5, 2006;

U.S. patent application Ser. No. 11/097,909, filed Apr. 1, 2005 for“Common Rail Fuel Injection System With Accumulator Injectors”,published as US/2006/0219220 on Oct. 5, 2006, now U.S. Pat. No.7,270,108, issued Sep. 18, 2007;

PCT application US2006/012353, filed Mar. 30, 2006 “Common Rail FuelInjection System With Accumulator Injectors”, published asWO/2006/107892 on Oct. 12, 2006;

US patent application Ser. No. 11/378,959, filed Mar. 17, 2006 for“Opposed Piston Engine”, published as US/2006/0157003 on Jul. 20, 2006,now US patent 7,360,511, issued Apr. 22, 2008;

U.S. patent application Ser. No. 11/629,136, filed Dec. 8, 2006, for“Improved Two Cycle, Opposed Piston Internal Combustion Engine”,published as US/2007/0245892 on Oct. 25, 2007;

U.S. patent application Ser. No. 11/642,140, filed Dec. 20, 2006, for“Two Cycle, Opposed Piston Internal Combustion Engine”;

U.S. patent application Ser. No. 12/075,374, filed Mar. 11, 2008, for“Opposed Piston Engine With Piston Compliance”, published asUS/2008/0163848 on Jul. 10, 2008; and,

U.S. patent application Ser. No. 12/075,557, filed Mar. 12, 2008, for“Internal Combustion Engine With Provision for Lubricating Pistons”.

BACKGROUND

The invention concerns an internal combustion engine. More particularly,the invention relates to a two-stroke, opposed-piston engine.

The opposed piston engine was invented by Hugo Junkers around the end ofthe nineteenth century. Junkers' basic configuration, shown in FIG. 1,uses two pistons P1 and P2 disposed crown-to-crown in a common cylinderC having inlet and exhaust ports I and E near bottom-dead-center of eachpiston, with the pistons serving as the valves for the ports. Bridges Bsupport transit of the piston rings past the ports I and E. The enginehas two crankshafts C1 and C2, one disposed at each end of the cylinder.The crankshafts, which rotate in the same direction, are linked by rodsR1 and R2 to respective pistons. Wristpins W1 and W2 link the rods tothe pistons. The crankshafts are geared together to control phasing ofthe ports and to provide engine output. Typically, a turbo-superchargeris driven from the exhaust port, and its associated compressor is usedto scavenge the cylinders and leave a fresh charge of air eachrevolution of the engine. The advantages of Junkers' opposed pistonengine over traditional two-cycle and four-cycle engines includesuperior scavenging, reduced parts count and increased reliability, highthermal efficiency, and high power density. In 1936, the Junkers Jumoairplane engines, the most successful diesel engines to that date, wereable to achieve a power density and fuel efficiency that have not beenmatched by any diesel engine since. According to C. F. Taylor (TheInternal-Combustion Engine in Theory and Practice: Volume II, revisededition; MIT Press, Cambridge, Mass., 1985): “The now obsolete Junkersaircraft Diesel engine still holds the record for specific output ofDiesel engines in actual service (Volume I, FIG. 13-11).”

Nevertheless, Junkers' basic design contains a number of deficiencies.The engine is tall, with its height spanning the lengths of four pistonsand at least the diameters of two crankshafts, one at each end of thecylinders. A long gear train with typically five gears is required tocouple the outputs of the two crankshafts to an output drive. Eachpiston is connected to a crankshaft by a rod that extends from theinterior of the piston. As a consequence the rods are massive toaccommodate the high compressive forces between the pistons andcrankshafts. These compressive forces, coupled with oscillatory motionof the wrist pins and piston heating, cause early failure of the wristpins connecting the rods to the pistons. The compressive force exertedon each piston by its connecting rod at an angle to the axis of thepiston produces a radially-directed force (a side force) between thepiston and cylinder bore. This side force increases piston/cylinderfriction, raising the piston temperature and thereby limiting the brakemean effective pressure (BMEP) achievable by the engine. One crankshaftis connected only to exhaust side pistons, and the other only to inletside pistons. In the Jumo engine the exhaust side pistons account for upto 70% of the torque, and the exhaust side crankshaft bears the heaviertorque burden. The combination of the torque imbalance, the wideseparation of the crankshafts, and the length of the gear train couplingthe crankshafts produces torsional resonance effects (vibration) in thegear train. A massive engine block is required to constrain the highlyrepulsive forces exerted by the pistons on the crankshafts duringcombustion, which literally try to blow the engine apart.

One proposed improvement to the basic opposed-piston engine, describedin Bird's U.K. Patent 558,115, is to locate the crankshafts beside thecylinders such that their axes of rotation lie in a plane thatintersects the cylinders and is normal to the axes of the cylinderbores. Such side-mounted crankshafts are closer together than in theJumo engines, and are coupled by a shorter gear train. The pistons andcrankshafts are connected by rods that extend from each piston along thesides of the cylinders, at acute angles to the sides of the cylinders,to each of the crankshafts. In this arrangement, the rods are mainlyunder tensile force, which removes the repulsive forces on thecrankshafts and yields a substantial weight reduction because a lessmassive rod structure is required for a rod loaded with a mainly tensileforce than for a rod under a mainly compressive load of the samemagnitude. The wrist pins connecting the rods to the pistons aredisposed outside of the pistons on saddles mounted to the outer skirtsof the pistons. Bird's proposed engine has torsional balance brought byconnecting each piston to both crankshafts. This balance, the proximityof the crankshafts, and the reduced length of the gear train producegood torsional stability. To balance dynamic engine forces, each pistonis connected by one set of rods to one crankshaft and by another set ofrods to the other crankshaft. This load balancing essentially eliminatesthe side forces that otherwise would operate between the pistons and theinternal bores of the cylinders. The profile of the engine is alsoreduced by repositioning the crankshafts to the sides of the cylinders,and the shorter gear train requires fewer gears (four) than the Jumoengine. However, even with these improvements, a number of problemsprevent Bird's proposed engine from reaching its full potential forsimplification and power-to-weight ratio (“PWR”, which is measured inhorsepower per pound, hp/lb).

The favorable PWR of opposed piston engines as compared with other twoand four cycle engines results mainly from the simple designs of theseengines which eliminate cylinder heads, valve trains, and other parts.However, reducing weight alone has only a limited ability to boost PWRbecause at any given weight, any increase in BMEP to increase power isconfined by the limited capability of the engines to cool the pistons.

Substantial combustion chamber heat is absorbed by pistons andcylinders. In fact the crown of a piston is one of the hottest spots ina two-cycle, opposed-piston compression-ignition engine. Excessivepiston heat will cause piston seizure. The piston must be cooled tomitigate this threat. In all high performance engines, the pistons arecooled principally by rings mounted to the outside surfaces of thepistons, near their crowns. The rings of a piston contact the cylinderbore and conduct heat from the piston to the cylinder, and therethroughto a coolant flowing through a cooling jacket or by cooling fins on theengine cylinder assembly. Intimate contact is required between the ringsand cylinder bore to cool the piston effectively. But piston rings mustbe lightly loaded in two-cycle, ported engines in order to survivetransit over the bridges of the cylinder ports, where very complexstresses occur. Therefore, the rings are limited in their ability tocool the pistons, which places a limit on the maximum combustion chambertemperature achievable before engine failure occurs. It is clear that,without more effective piston cooling, BMEP cannot be increased in anopposed piston engine without endangering the engine's operation.

Prior engines include an engine block in which cylinders and enginebearings are cast in a large passive unit that serves as the primarystructural and architectural element of the engine. Although Bird'sengine rectified torque imbalance, eliminated compressive forces on therods, and eliminated side forces on the cylinder bore, it still used theengine block as the primary structural element, providing support forthe cylinders, manifolds for cylinder ports, and cooling jackets for thecylinders and for retaining the engine bearings. But thermal andmechanical stresses transmitted through the engine block causenon-uniform distortion of the cylinders and pistons necessitating pistonrings to assist in maintaining the piston/cylinder seal.

SUMMARY

In one aspect, increased BMEP is realized in a two-stroke,opposed-piston engine with side-mounted crankshafts and optimized pistoncooling. In this engine, pistons are substantially withdrawn from acylinder during engine operation to be cooled externally of the cylinderby direct application of coolant onto outside surface portions of thepistons.

In another aspect, rather than forming an architectural or structuralcomponent of the engine, the cylinder acts primarily as a pressurevessel that contains the forces of combustion.

In yet another aspect, the cylinder and pistons are substantiallyradially symmetric and free of non-uniform radial thermal and mechanicalstress along their axial lengths. Combined with improved piston cooling,this characteristic permits optional ringless operation. Without rings,inlet and exhaust port design can be simplified by elimination ofbridges. The resulting large port areas and absence of flow-impedingstructures permit high volumetric flow efficiency and support excellentscavenging, further improving power output.

These improvements, and other improvements and advantages described inthe specification which follows, provide a very simple two-stroke,opposed-piston, engine capable of a substantial increase in BMEP, andwith reduced weight, resulting in an engine capable of BMEP and PWR muchhigher than attained by comparable prior art engines of the same speed.

BRIEF DESCRIPTION OF THE DRAWINGS

The below-described drawings are meant to illustrate principles andexamples discussed in the following detailed description. They are notnecessarily to scale.

FIG. 1 is a partially schematic illustration of a portion of a prior artopposed piston diesel engine.

FIGS. 2A and 2B are side sectional views of a cylinder with opposedpistons coupled by tensile-loaded connecting rods to two crankshafts.FIG. 2A shows the pistons at inner, or top dead center. FIG. 2B showsthe pistons at outer, or bottom dead center.

FIGS. 3A-3F are schematic sectional illustrations of the cylinder andpistons of FIGS. 2A and 2B illustrating a complete cycle of the pistons.

FIG. 4 is a plot showing relative phasing of the two opposed pistons ofFIGS. 3A-3F.

FIG. 5A is a side sectional view of the cylinder with opposed pistons ofFIGS. 2A and 2B rotated 90° on its axis. FIG. 5B is the same view of thecylinder in FIG. 5A showing an alternate embodiment for cooling thecylinder.

FIGS. 6A and 6B are side perspective views showing increasingly completestages of assembly of a single cylinder mechanism for an opposed-pistonengine.

FIGS. 7A-7C are perspective views of a single-cylinder opposed-pistonengine module showing assembly details at increasingly complete stagesof assembly. FIG. 7D is an end view of the single-cylinderopposed-piston engine module showing an open gearbox with one gearpartially cut away.

FIGS. 8A-8C are perspective views of a multiple-cylinder opposed-pistonengine module showing assembly details at increasingly complete stagesof assembly.

FIG. 9A is a schematic diagram of a supply system for an opposed-pistonengine which provides liquid coolant to the engine. FIG. 9B is aschematic diagram of a combined fuel and coolant supply system for anopposed-piston engine. FIG. 9C is a schematic diagram of another supplysystem for an opposed-piston engine which provides liquid coolant to theengine.

FIG. 10 is a schematic diagram of gas flow in an opposed-piston engine.

FIGS. 11A-11F illustrate applications of the opposed-piston engine.

DETAILED DESCRIPTION

Components of our new opposed piston engine are illustrated in FIGS. 2Aand 2B. These figures show a cylinder 10 with opposed pistons 12 and 14disposed therein. The pistons 12 and 14 move coaxially in the cylinder10 in opposed motions, toward and away from each other. FIG. 2Aillustrates the pistons 12 and 14 at top (or inner) dead center wherethey are at the peak of their compression strokes, near the moment ofignition. FIG. 2B illustrates the pistons near bottom (or outer) deadcenter, where they are at the end of their expansion or power strokes.These and intermediate positions will be described in more detail below.

The following explanation presumes a compression-ignition engine for thesake of illustration and example only. Those skilled in the art willrealize that the elements, modules and assemblies described may also beadapted for a spark-ignition engine.

As shown in FIGS. 2A and 2B, the cylinder 10 is a tube with the opposedpistons 12 and 14 disposed in it for reciprocating opposed motion towardand away from each other and the center of the cylinder 10. The pistons12 and 14 are coupled to first and second side-mounted counter-rotatingcrankshafts 30 and 32 which, in turn, are coupled to a common output(not shown in these figures).

The pistons 12 and 14 are hollow cylindrical members with closed axialends 12 a and 14 a which terminate in crowns 12 d and 14 d, open axialends 12 o and 14 o, and skirts 12 s and 14 s which extend from the openaxial ends 12 o and 14 o to the crowns 12 d and 14 d. Saddles 16 and 18,in the form of open annular structures, are mounted to the open axialends 12 o and 14 o of the pistons 12 and 14, respectively. Each of thesaddles 16, 18 connects ends of a plurality of connecting rods to therespective piston on which it is mounted. The perspective of thesefigures illustrates only two connecting rods for each piston, and it isto be understood that one or more additional connecting rods are notvisible. The connecting rods 20 a and 20 b are connected to the saddle16 near the open end of the piston 12, while the connecting rods 22 aand 22 b are connected to the saddle 18 near the open end of the piston14. Because the saddles 16 and 18 provide linkage between the pistons 12and 14 and their respective rods, the pistons lack internal wristpins.The resulting open structure of the saddles and the pistons permitscoolant dispensers 24 and 26 to extend axially into the pistons 12 and14 from the open ends 12 o and 14 o to be aimed at the crowns andinternal skirts of the pistons 12 and 14, respectively.

The two side-mounted crankshafts 30 and 32 are disposed with their axesparallel to each other and lying in a common plane that intersects thecylinder 10 at or near its longitudinal center and that is perpendicularto the axis of the cylinder. The crankshafts rotate in oppositedirections. The connecting rods 20 a, 20 b and 22 a, 22 b are connectedto crank throws on the crankshafts 30 and 32. Each connecting rod isdisposed to form an acute angle with respect to the axes (and the sides)of the cylinder 10 and the pistons 12 and 14. The connecting rods arelinked to the saddles 16 and 18 by means of needle bearings 36, and tothe crank throws by means of roller bearings 38. As each piston movesthrough the operational cycle of the engine, the ends of the connectingrods coupled to the piston's saddle oscillate through an angular path,and there is no complete revolution between those ends and the elementsof the saddle to which they are coupled. Needle bearings withsufficiently small diameter rollers produce at least full rotation ofthe rollers during each oscillation, thereby reducing wear asymmetry andextending bearing life.

The geometric relationship between the connecting rods, saddles, andcrankshafts in FIGS. 2A and 2B keeps the connecting rods principallyunder tensile stress as the pistons 12 and 14 move in the cylinder 10,with a limited level of compressive stress resulting from inertialforces of the pistons at high engine speeds. This geometry reduces orsubstantially eliminates side forces between the pistons and the bore ofthe cylinder.

In FIGS. 2A and 2B, additional details and features of the cylinder 10and the pistons 12 and 14 are shown. The cylinder 10 includes an inletport 46 through which air, under pressure, flows into the cylinder 10.The cylinder also has an exhaust port 48 through which the products ofcombustion flow out of the cylinder 10. Because of their locations withrespect to these ports, the pistons 12 and 14 may be respectivelyreferred to as the “exhaust” and “inlet” pistons, and the ends of thecylinder 10 may be similarly named. A preferred, but by no means theonly possible, configuration for the ports 46 and 48 are describedbelow. The operations of the exhaust and inlet ports are modulated bymovement of the pistons during engine operation. At least one injectionsite (not shown in this drawing) controlled by one or more fuelinjectors (described below) admits fuel into the cylinder 10.

As the following illustrations and description will establish, therelation between piston length, the length of the cylinder, and thelength added to the cylinder bore by the cylinder manifolds, coupledwith a phase difference between the pistons as they traverse theirbottom dead center positions, modulate port operations and sequence themcorrectly with piston events. In this regard, the inlet and exhaustports 46 and 48 are displaced axially from the longitudinal center ofthe cylinder, near its ends. The pistons may be of equal length. Eachpiston 12 and 14 keeps the associated port 46 or 48 of the cylinder 10closed until it approaches its bottom dead center position. The phaseoffset between the bottom dead center positions produces a sequence inwhich the exhaust port opens when the exhaust piston moves near itsbottom dead center position, then the inlet port opens when the inletpiston moves near its bottom dead center position, following which theexhaust port closes after the exhaust piston moves away from its bottomdead center position, and then the inlet port closes after the inletpiston moves away from its bottom dead center position.

FIGS. 3A-3F are schematic representations of the cylinder 10 and pistons12 and 14 of FIGS. 2A and 2B illustrating a representative cycle ofoperation (“operational cycle”). In this example, with the pistons attop dead center, the opposing rods on each side of the cylinder form anangle of approximately 120° as shown in FIG. 3A. This geometry is merelyfor the purpose of explaining an operational cycle; it is not meant toexclude other possible geometries with other operating cycles. Forconvenience, an operational cycle may be measured rotationally, startingat a crank angle of 0° where the pistons are at top dead center as shownin FIG. 3A and ending at 360°. With reference to FIG. 3A, the term “topdead center” is used to refer to the point at which the closed ends 12 aand 14 a of the pistons 12 and 14 are closest to each other and to thecrankshafts and air is most highly compressed in the cylinder space 42between the ends. This is the top of the compression stroke of bothpistons. Using a convenient measurement, top dead center occurs at 0° ofthe cycle of operation. Further, with reference to FIGS. 3C and 3E, theterm “bottom dead center” refers to the points at which the closed ends12 a and 14 a of the pistons 12 and 14 are farthest from the crankshafts30 and 32. Bottom dead center for the piston 12 occurs just before 180°of the cycle of operation. Bottom dead center for the piston 14 occursjust after 180° of the cycle of operation.

A two-stroke, compression-ignition operational cycle is now explainedwith reference to FIGS. 3A-3F. This explanation is meant to beillustrative, and uses 360° to measure a full cycle. The events andactions of the cycle are referenced to specific points in the 360° cyclewith the understanding that for different geometries, while the sequenceof events and actions will be the same, the points at which they occurin the 360° cycle will differ from those in this explanation.

Referring now to FIG. 3A, prior to the 0° reference point in theoperational cycle where the pistons 12 and 14 will be at top deadcenter, fuel is initially injected into the cylinder through the atleast one injection site. Fuel may continue to be injected aftercombustion commences. The fuel mixes with compressed air and the mixtureignites between the closed ends 12 a and 14 a, driving the pistons apartin a power stroke, to drive the crankshafts 30 and 32 to rotate inopposite directions. The pistons 12 and 14 keep the inlet and exhaustports 46 and 48 closed during the power stroke, blocking air fromentering the inlet port and exhaust from leaving the exhaust port. InFIG. 3B, at 90° in the operational cycle, the pistons 12 and 14, nearmidway through their power strokes, continue to travel out of thecylinder 10. The inlet and exhaust ports 46 and 48 are still closed. InFIG. 3C, at 167° in the operational cycle, the closed end 12 a of thepiston 12 has moved far enough out of the cylinder 10 to open theexhaust port 48, while the inlet port 46 is still closed. The productsof combustion now begin to flow out of the exhaust port 48. This portionof the cycle is referred to as blow-down. In FIG. 3D, at 180° in theoperational cycle, the inlet and exhaust ports 46 and 48 are open andpressurized air flows into the cylinder 10 through the inlet port 46,while exhaust produced by combustion flows out of the exhaust port 48.Scavenging now occurs as residual combustion gasses are displaced withpressurized air. In FIG. 3E, at 193° the exhaust port 48 is closed bythe piston 12, while the inlet port 46 is still open due to the phaseoffset described above and explained in more detail below. Charge aircontinues to be forced into the cylinder 10 through the inlet port 46until that port is closed, after which the compression stroke begins. At270° in the operational cycle, shown in FIG. 3F, the pistons 12 and 14are near halfway through their compression stroke, and both the inletand exhaust ports 46 and 48 are closed. The pistons 12 and 14 then againmove toward their top dead center positions, and the cycle iscontinually repeated so long as the engine operates.

FIG. 4 is a plot showing the phases of the pistons 12 and 14 during therepresentative operational cycle just described. Piston phase may bemeasured at either crankshaft referenced to the top dead center of eachpiston. In FIG. 4, the axis AA represents the distance of the crown of apiston from its top dead center position, and the axis BB representsphase. The position of the piston 12 is indicated by the line 50, whilethat of the piston 14 is indicated by the line 52. At top dead center60, both of the pistons are in phase and the closed ends 12 a and 14 aare equally distant from the longitudinal center of the cylinder 10. Asthe operational cycle proceeds, the piston 12 increasingly leads inphase until it reaches its bottom dead center point 61, just before 180°in the operational cycle, indicated by 62. After the 180° point, thepiston 14 passes through its bottom dead center point 63 and begins tocatch up with the piston 12 until the two pistons are once again inphase at 360° in the cycle.

The oscillating phase offset between the pistons 12 and 14 illustratedin FIG. 4 enables the desired sequencing of the inlet and exhaust ports46 and 48. In this regard, the line CC in FIG. 4 represents the positionof the crown of a piston where the port controlled by the piston opens.Thus, when the closed end 12 a of the piston 12 reaches the pointrepresented by 64 on CC, the exhaust port only begins to open. When theclosed end 14 a of the piston 14 moves past the point represented by 65on CC, both ports are open and scavenging takes place. At 67 on CC, theexhaust port closes and cylinder air charging occurs until the pistonend 14 a reaches the point represented by 68 on CC when both ports areclosed and compression begins. This desirable result arises from thefact that the connecting rods for the respective pistons travel throughdifferent paths during crankshaft rotation; while one rod is going overthe top of one crankshaft, the other is rotating under the bottom of thesame crankshaft.

It should be noted with respect to FIG. 4 that the respective openingpositions for the exhaust and inlet ports may not necessarily lie on thesame line and that their relative opening and closing phases may differfrom those shown.

As seen in FIGS. 2A, 2B, and 5A, the cylinder 10 includes a cylindertube 70 with opposing axial ends and annular exhaust and intakemanifolds 72 and 74, each threaded, welded, or otherwise joined to arespective axial end of the cylinder tube 70. The manifolds 72 and 74may be denominated the “cylinder exhaust manifold” and the “cylinderinlet manifold”, respectively. The manifolds 72 and 74 have respectiveinternal annular galleries 76 and 78 that constitute the exhaust andinlet ports, respectively. Preferably each of the galleries 76 and 78has the shape of a scroll in order to induce swirling of gasses flowingtherethrough, while inhibiting turbulent mixing. Swirling thepressurized air facilitates scavenging and enhances combustionefficiency. The cylinder manifold 72 also includes an annular passage 77surrounding the annular gallery 76. The annular passage 77 may beconnected to receive airflow, or alternatively it may contain stagnantair, to cool the periphery of the manifold 72. When the cylindermanifolds 72 and 74 are joined to the cylinder tube 70, their outerportions extend the bore of the tube. The common bore may be precisionmachined to closely match the diameter of the pistons 12 and 14, and thepistons and cylinder may be fabricated from materials with compatiblethermal expansion characteristics. If ringless pistons (pistons withoutrings) are used, there is no need for bridges spanning the ports, and avery close tolerance may be obtained between the outer diameters of thepistons and the inner diameter of the common bore. With ringlessoperation, for example, the spacing between each piston and the bore maybe on the order of 0.002″ (2 mils or 50 microns), or less. The absenceof bridges also facilitates the formation of the intake manifold 74 intoa swirl inducing shape such as a scroll. If, on the other hand, thepistons are provided with rings, it will be necessary to form theexhaust and inlet ports as annular passages with annular sequences ofopenings to the tube 70, thereby providing bridges to support thetransit of the rings past the ports. Tubes 82 and 84 formed on thecylinder manifolds 72 and 74 open into the internal annular galleries 76and 78, providing connection between the exhaust and inlet ports andrespective exhaust and inlet manifolds.

FIG. 5A is an enlarged side sectional view of the cylinder 10 withopposed pistons 12 and 14 at their respective positions when theoperational cycle is near its 180° point. As shown in these figures, thepistons 12 and 14 are provided without piston rings, although they maybe provided with rings if dictated by design and operation. Piston ringsare optional elements in this engine, for two reasons. First, pistonrings accommodate radial distortion of pistons and cylinders in order toassist in controlling the cylinder/piston seal during engine operation.However, the cylinders illustrated and described in this specificationare not cast in an engine block and are therefore not subject tonon-uniform distortion from any thermal stress or any mechanical stressgenerated by other engine components, or asymmetrical cooling elements.As a result the cylinders and pistons may be machined with very tighttolerances for very close fitting, thereby confining combustion andlimiting blow-by of combustion products along the interstice betweeneach piston and the cylinder. Second, piston rings act to cool thepiston during engine operation. However, while the engine operates, eachpiston may be cooled by application of liquid coolant because eachpiston is periodically substantially entirely withdrawn from (orprotrudes from) the cylinder as it moves through its bottom dead centerposition so that liquid coolant can be applied to its external surface.See FIGS. 2B, 3C and 5A in this regard. As a piston moves out of andback into the cylinder, it is showered (by dispensers to be described)with a liquid coolant on the outer surface of its skirt. In addition,liquid coolant is applied (by a dispenser 24 or 26) to its inner surfacealong its skirt up to and including its crown.

For example, in FIGS. 5A and 6A, each piston 12 and 14 is substantiallywithdrawn from the cylinder 10 near its bottom dead center position.Taking the piston 12 as representative, this means that, with the closedend 12 a of the piston 12 near the outer edge of the annular gallery 76,the skirt 12 s of the piston 12 is substantially entirely withdrawn fromthe cylinder 10 while only the portion of the piston crown 12 d betweenthe outside edge 76 o of the gallery 76 and the outside edge 72 o of theexhaust manifold 72 remains in the exhaust manifold 72 fitted on the endof the cylinder 10 as described below. It should be noted that eachpiston 12 and 14 subsequently moves back into the cylinder 10 to theextent that it is substantially enclosed by the cylinder 10 when itreaches its top dead center position.

Thus, at its bottom dead center position, substantially the entire skirtof each piston 12 and 14 protrudes from the cylinder 10 and is exposedfor cooling. The detailed description of how that occurs in thisillustrative example is not meant to limit the scope of this feature;what is required is that enough of the outside surface of the skirt ofeach of the pistons 12 and 14 be periodically outside of the cylinder 10during engine operation to be sufficiently cooled by application of acoolant to the outside surfaces of the skirts outside of the cylinder.The percentage of the piston skirt that is exposed in a particularapplication may vary based on a number of factors including, forexample, system coolant requirements, engine geometry, and designerpreference.

As a piston moves in and out of a cylinder it is cooled by applicationof a liquid coolant (by dispensers to be described) to the outer surfaceof its skirt. In addition, liquid coolant is applied (by dispenser 24 or26) to its inner surface along its skirt up to and including its crown.The same liquid coolant is preferably used to cool both the interior andthe exterior of the pistons. With reference to FIGS. 5A and 6A, coolantdispensers, preferably made of steel tubing, dispense a liquid coolantonto the pistons 12 and 14 and the cylinder 10 during engine operation.An elongate dispenser manifold 86 extends at least generally axiallyalong and against the cylinder tube and exhaust and inlet manifolds 72and 74. Four axially spaced semicircular dispensers 86 a, 86 b, 86 c,and 86 d extend from the manifold tube halfway around the cylinder 10.The dispenser 86 a is positioned outboard of the center of the exhaustmanifold 72, near the outside edge 72 o; the two dispensers 86 b and 86c are located over the cylinder 10 between the manifolds 72 and 74,preferably near the axial center of the cylinder 10 in order to applyproportionately more liquid coolant to the hottest region of thecylinder than to other, cooler regions nearer the manifolds 72 and 74;and the dispenser 86 d is located outboard of the center of the inletmanifold 74, near the outside edge 74 o. A second dispenser manifoldtube 88 extends at least generally axially along and against thecylinder tube and exhaust and inlet manifolds 72 and 74. Four axiallyspaced semicircular dispensers 88 a, 88 b, 88 c, and 88 d extend fromthe manifold tube 88 halfway around the cylinder 10. The dispenser 88 ais positioned outboard of the center of the exhaust manifold 72, nearthe outside edge 72 o; the two dispensers 88 b and 88 c are located overthe cylinder between the manifolds 72 and 74, preferably near the axialcenter of the cylinder 10 in order to apply proportionately more liquidcoolant to the hottest region of the cylinder than to other, coolerregions nearer the manifolds 72 and 74; and the dispenser 88 d islocated outboard of the center of the inlet manifold 74, near theoutside edge 74 o. Opposing dispensers are linked together as at 89 forstructural integrity. Alternatively, the dispensers may be entirelycircular and connected to a single manifold tube. Further, fewer or moredispensers may be provided and may be differently positioned than asshown. Still further, the dispensing branches could be replaced by anumber of circumferentially spaced nozzles or sprayers supplied withliquid coolant from a common source.

The dispensers have substantial apertures formed thereinto from which aliquid coolant under pressure is applied to exposed outside surfaces ofthe skirts of the pistons 12 and 14 and the outside surface of thecylinder tube 70. Preferably, dispensers are positioned near therespective outside edges of the manifolds in order to ensure that liquidcoolant is applied to substantially the entire outside surface of theskirt along the axial length of each piston. Depending on factors suchas system coolant requirements, engine geometry and designer preference,the dispensers, nozzles, or other suitable coolant application elementsmay be repositioned in order to dispense or apply liquid coolant tosmaller percentages of the outer radial peripheral surface areas of theskirts. For example, liquid coolant may be applied to the outside orexternal surface of the skirt along at least 25%, 50%, or 75% of theaxial length of each piston.

In FIGS. 5A and 6A, the liquid coolant dispensers that apply liquidcoolant to the outside surfaces of the pistons and cylinder are shown asbeing separate elements; however, one or more dispensers may also beintegral with the cylinder manifolds 72 and 74 in addition to, orinstead of, the separate elements shown in the figures.

In an alternate embodiment shown in FIG. 5B, instead of cooling thecylinder tube 70 by way of dispensers, the cylinder tube may be disposedin a jacket 87 to provide a cooling passage 90 around the cylinderthrough which the coolant may be circulated. In this case, dispenserswould still be used to cool the pistons.

The open structure of the saddles 16 and 18 and the absence of wristpinsin the pistons permit improved direct application of liquid coolant tothe internal surfaces of the pistons. In this regard, as shown in FIGS.2A, 2B, and 5A, the pistons 12 and 14 are continuously cooled duringengine operation by application of liquid coolant through dispensers 24and 26 to their interior surfaces including their domes along theirskirts to their open axial ends.

In FIG. 5A, the flow of liquid coolant onto the pistons and the cylinderis indicated by reference numeral 91.

Continuing with the description of FIG. 5A, annular, high-temperaturepolymeric rings 92 located in annular grooves near the ends of themanifolds 72 and 74 lightly contact the pistons 12 and 14 and wipeexcess lubricant from the pistons as they travel into the cylinder 10.Finally, one or more fuel injectors are provided for the cylinder. Forexample, the fuel injector 94 is coupled to the at least one injectionsite 95.

A two-stroke, opposed-piston engine mechanism is next described in whichthe working elements (cylinders, pistons, linkages, crankshafts, etc.)are received upon a structural unit in the form of a frame of passivestructural elements fitted together to support the working elements. Theframe is intended to bear the stresses and forces of engine operation,such as compressive forces between the crankshafts. In contrast withmany prior art two-cycle, opposed-piston engines, the cylinders are notcast in a block nor are they formed with other passive structuralelements. Consequently, the cylinders are not passive structuralelements of the engine. Each cylinder is supported in the engine frameprincipally by the pair of pistons disposed in it. Thus, with theexception of combustion chamber forces, the cylinders are decoupled fromthe mechanical stresses induced by functional elements, and from themechanical and thermal stresses of an engine block. Hence, the cylindersare essentially only pressure vessels. This engine constructioneliminates non-uniform radial distortion of the pistons and cylinders,permits the cylinder-piston interface to be very close-fitting, andenables a close matching of the thermal characteristics of the materialsfrom which the cylinders and pistons are made. Advantageously, withimproved piston cooling, this characteristic affords the option of anengine design that dispenses with piston rings.

FIGS. 6A and 6B are side perspective views showing increasingly completeassembly of a single-cylinder engine mechanism 100 for an opposed-pistonengine with side-mounted crankshafts based on the cylinder/pistonarrangement of the previous figures. The engine mechanism 100 can bescaled to engines of any size and engines having from one to multiplecylinders. In FIG. 6A, the mechanism 100 includes a single cylinder 10having the construction illustrated in FIG. 5A, with opposed pistons 12and 14 disposed in it. The saddles 16 and 18 of the opposed pistons arevisible in the figure. The connecting rods 20 a and 20 c couple thesaddle 16 to the crankshaft 30, and the connecting rod pair 20 b couplesthe saddle 16 to the crankshaft 32. The connecting rod pair 22 a couplesthe saddle 18 to the crankshaft 30, and the connecting rods 22 b and 22c couple the saddle 18 to the crankshaft 32. The dispenser manifold tube88 and the dispenser 24 are connected to coolant manifold 96. Themanifold tube 86 and the dispenser 26 are connected to another coolantmanifold 98. Two radially-opposed alignment pins (one of which isindicated by reference numeral 99) are formed on the cylinder 10 forcylinder stabilization during engine operation. Two beams 110 and 112are shown in FIG. 6A for reference. The beam 110 has an opening 113through which the manifold tube 84 can be connected to an air inletmanifold (not shown) and an opening 115 for a tube connecting the fuelinjector 94 to a fuel manifold (not shown). The beam 112 has an opening117 through which the manifold tube 82 can be connected to an exhaustmanifold (not shown) and an opening 119 through which a tube can connectanother fuel injector (not seen) to a fuel manifold (not shown).

In FIG. 6B, a frame for the engine mechanism 100 includes two supportbulkheads 120 disposed on respective sides of the cylinder 10, togetherwith the beams 110 and 112. The bulkheads 120 receive and support thecrankshafts 30 and 32. Each bulkhead 120 includes an I-beam section 122and a transverse section 124. The I-beam sections provide the principalsupport for the crankshafts during engine operation. The beams 110 and112 are attached to the ends of the transverse sections 124. Thecrankshafts are supported for rotation in the I-beam sections 122 bybearings 128. Each bulkhead includes a central opening with a shortelastomeric cylinder 132 that receives alignment pins 99 of adjacentcylinders. Threaded holes 134 are provided in each support bulkhead forattachment of additional components, for example, a gearbox.

Assembly of a single-cylinder opposed piston engine module from theengine mechanism 100 of FIGS. 6A and 6B is shown in FIGS. 7A-7D. In thesingle-cylinder engine module, light aluminum end plates 160 and 162 areattached to respective bulkheads 120 and to each of the beams 110 and112. The end plate 160 has openings 163 and 164 to receive the liquidcoolant manifolds 96 and 98 to feed lines (not shown). FIGS. 7A-7D showa gearbox 170 mounted on a bulkhead (not seen in these figures) throughthe outside surface of the end plate 160. The gearbox 170 houses anoutput gear train through which the opposing rotational motions of thecrankshafts are coupled to an output drive shaft. The ends of thecrankshafts 30 and 32 extend into the gearbox 170. A gear wheel 172 witha toothed outer rim is fixed to the end of the crankshaft 30 and a gearwheel 173 with a toothed outer rim is fixed to the end of the crankshaft32. An output gear wheel 175 has an annulus 176 with a toothed insidecircumference 177 and a toothed outside circumference 178. As seen inthese figures, the outer rim of the gear wheel 172 engages the insidecircumference 177 of the output gear wheel 175 at one location and theouter rim of the gear wheel 173 engages the outside circumference 178 ofthe output gear wheel 175 at another location diametrically opposite theone location. The gear ratio between the inner gear 172 and the insidecircumference 177 may be 33/65 with MOD 4 teeth on the inner gear andthe inside circumference, while the gear ratio between the outer gear173 and the outside circumference 178 may be 33/65 with MOD 5 teeth onthe outer gear and the outside circumference. This arrangement of gearspermits the opposing rotations of the crankshafts 30 and 32 to betranslated into the continuous rotation of the output gear wheel 175with an odd number of gears (three, in this case), with a non-integralgear ratio, and without any intermediary belts, chains, or other torquetransfer elements. The result is a simple, short output gear train.

Assembly of the single-cylinder opposed piston engine module iscompleted as shown in FIGS. 7A-7D by attachment of light aluminum casingpanels 180 to the frame made up of the assembled bulkheads and beams. Acover 182 is fastened to the gearbox 170. The cover 182 includes anoutput bearing 185 that receives the axle 186 of the output gear wheel175 thus enabling the frame to support the output gear 175 for rotation.The resulting assembled single-cylinder opposed-piston engine module isindicated by reference numeral 190 in FIG. 7C. The axle 186 constitutesthe output drive of the engine module 190. It may be coupled to anintermediate transmission or directly to the driven component by one ormore gears, belts, chains, cams or other suitable torque transferelement or system (not shown).

FIGS. 8A-8C illustrate assembly of a multi-cylinder, opposed-pistonengine module with three engine mechanisms 100 disposed in a row. Notethat the front and rear bulkheads are removed from FIG. 8A for clarity.The mechanisms 100 have the structure already illustrated in FIGS. 6Aand 6B, and discussed in respect of the preceding figures. Fourbulkheads 120 are provided in the frame of this engine module, eachsupporting the crankshafts in respective bearings. The frame alsoincludes elongated beams 110 and 112 fixed to the transverse sections ofthe bulkheads 120. The end plates 160 and 162 close the ends of theengine module. The three-gear drive train is supported for rotation inthe gearbox 170. The liquid coolant manifolds 96 and 98 are elongated tospan the three engine mechanisms 100. Assembly of the multiple-cylinderopposed piston engine module is completed by attachment of lightaluminum casing panels 180 to the frame. A cover 182 is fastened to thegearbox 170. The cover 182 includes an output bearing 185 that receivesthe axle 186 of the output gear wheel 175 thus enabling the frame tosupport the output gear wheel 175 for rotation. The resulting assembledmultiple-cylinder opposed-piston engine module is indicated by referencenumeral 290 in FIG. 8C. The axle 186 constitutes the output drive of theengine module 290.

The best mode for carrying out an opposed-piston internal combustionengine according to the principles thus far described and illustratedincludes providing four identical connecting rods for each piston. Thismode of practice is best seen in FIG. 6A. In the view of FIG. 6A, on theexhaust port side of the cylinder 10, the two connecting rods 20 a and20 c are spaced apart and each is connected at one end to the saddle 16and at the opposite end to the crankshaft 30. The connecting rod pair 20b comprises two abutting rods, each identical in shape and structure tothe rods 20 a and 20 c. The connecting rod pair 20 b is connected at oneend to the saddle 16, and at the other end to the crankshaft 32. On theinput port side of the cylinder 10, the two connecting rods 22 b and 22c are spaced apart and each is connected at one end to the saddle 18 andat the opposite end to the crankshaft 32 on either side of theconnecting rod pair 20 b. The connecting rod pair 22 a comprises twoabutting rods, each identical in shape and structure to the rods 22 band 22 c. The connecting rod pair 22 a is connected at one end to thesaddle 18, and at the other end to the crankshaft 30, between theconnecting rods 20 a and 20 c. Thus, on each of the crankshafts, theconnecting rod pairs of the pistons on one end of the cylinders areinterleaved with the two connecting rods of the pistons on the other endof the cylinders, as shown in FIG. 6A. This provides an optimum balanceof forces on the pistons and also reduces the count of part types forthe engine. The identical rods also assist in maintaining uniformthermal expansion of the rods during engine operation.

The best mode also includes connecting rods of forged steel or titanium,cylinders and pistons of aluminum-silicon alloy with chrome-platedcylinder bores, liquid coolant-conducting elements of steel tubing, andcrankshafts of forged, machined steel. Engine frame parts may be made oflightweight alloys such as aluminum.

A supply system 300 for supplying a liquid coolant to be dispensed onand in pistons and on cylinders in an opposed-piston engine of one ormore cylinders is illustrated in FIG. 9A. The liquid coolant may be anyliquid capable of being applied to the pistons and cooling themsufficiently for the desired application. Lubricating oil and dieselfuel are two possibilities. In this figure, a source of liquid coolant310 is connected to a low-pressure, high-volume pump 312. The pump 312may comprise, for example, a centrifugal pump providing liquid coolantin the range of 3 to 10 gal/min for a 100 HP engine. which pumps liquidcoolant through a distribution line 313 to the manifolds 96 and 98.These manifolds supply a high volume of liquid coolant at low pressureto the dispensers 24 and 26 and to the dispensing manifolds 86 and 88 ofone or more modules 100. The liquid coolant is collected by a sump 315in the opposed-piston engine. A pump 317 connected to the sump pumps thecollected liquid coolant through a filter 318 and a radiator 319 back tothe source 310. As seen in FIG. 9A, a line 320 may be provided inparallel with the radiator 319. In this case, a valve 321 would controlliquid coolant flow through the radiator 319 and a valve 322 wouldcontrol liquid coolant flow through the line 320. For normal operation,only the valve 321 would be open, permitting liquid coolant to flowthrough the radiator 319, thereby dissipating the heat of the pistonsand cylinders via the radiator 319. For short term boosted operation,the valves 321 and 322 would both be open, thereby dissipating the heatof the pistons and the cylinders via the radiator 319 and absorbing someof the heat in the reservoir of liquid coolant in the source 310.Finally, during emergency operation in the event of radiator failure thevalve 321 would be closed and the valve 322 would be open, therebytemporarily diverting the heat of the pistons and cylinders into thereservoir of liquid coolant.

If an opposed-piston engine is operated as a compression-ignitionengine, fuel injection is the method of delivering diesel fuel to thecylinders for combustion. In this case, diesel fuel also preferablyserves as the liquid coolant and as the lubricant for the pistons. It istherefore possible to combine the fueling and coolant sources,eliminating the need for multiple sources. Referring to FIG. 9B, asystem 400 for supplying diesel fuel to be dispensed on and in pistonsand on cylinders and supplied to fuel injectors in an opposed-pistonengine of one or more cylinders is illustrated. In this figure, a sourceof diesel fuel 410 is connected to a low-pressure, high-volume pump 412(a centrifugal pump, for example) which pumps liquid coolant through adistribution line 413 to the manifolds 96 and 98. These manifolds supplya high volume of liquid coolant at low pressure to the dispensers 24 and26 and to the dispensing manifolds 86 and 88 of one or more enginemechanisms 100. The diesel fuel is collected by a sump 415 in theopposed-piston engine. A pump 417 connected to the sump pumps thecollected diesel fuel through a filter 418 and a radiator 419 back tothe source 410. A return line 420 parallel to the radiator 419 isprovided. Valves 421 and 422 control the use of the radiator 419 andreturn line 420 as explained above in connection with the valves 321 and322 in FIG. 9A. A pre-pump 423 connected to the source 410 pumps dieselfuel through a filter 424, and to a high-pressure pump 426, which booststhe pressure of fuel delivered to the injectors. For example, the pump426 may supply diesel fuel at 30,000 psi. The fuel from the pump 426 issupplied through an input fuel line 427 connected to a common rail 429and the input ports of one or more fuel injectors 94. The return portsof the one or more fuel injectors are returned through line 430 to thesource 410. An electronic control unit (ECU) 431 controls the operationsof the one or more fuel injectors 94.

Another advantage of an engine built according to this specification isthat all of the bearings used to support the crankshafts and connectingrods may be roller bearings. These bearings may be lubricated by beingsprayed with diesel fuel, whose lubricity and viscosity at the operatingtemperatures of an opposed-piston engine are completely adequate fortheir lubrication.

Thus, by way of the pump 412, the system 400 may deliver diesel fuel asa lubricant for all bearings of the engine, save those in the gearbox170. In this regard, as diesel fuel supplied from the dispensers, thediesel fuel is churned into a mist within the engine that spreadsthroughout the engine and works its way between the moving parts of theengine and into the rolling bearings contained within the engine. Asingle source can then be used to supply such coolant, and lubricant tothe engine.

An alternate supply system 350 for supplying a liquid coolant to bedispensed on and in pistons and on cylinders in an opposed-piston engineof one or more cylinders is illustrated in FIG. 9C. This system may beused for dispensing liquid coolant alone as the system 300 in FIG. 9A,or it may be combined with other elements in a system for dispensingdiesel fuel to cool, lubricate, and fuel an engine as illustrated inFIG. 9B. The liquid coolant may be any liquid capable of being appliedto the pistons and cooling them sufficiently for the desiredapplication. Lubricating oil and diesel fuel are two possibilities. Inthis figure, an engine enclosure 352 enclosing one or more enginemechanisms 100 contains a sump region 357 where liquid coolant emittedby the above-described dispensers is collected. The liquid coolantcollected in the sump region 357 has a nominal operating fluid level358. A source valve 359 is mounted in the engine enclosure. A levelsensor 360 in contact with the liquid coolant collected in the sumpregion 357 controls a linkage 361 that selects the state of the sourcevalve 359. The source valve 359 has an output connected to alow-pressure high-volume pump 362. The pump 362 may comprise, forexample, a centrifugal pump. The source valve 359 has two inputs, afirst connected to a feed line 363 from the sump region 358, and asecond connected to a feed line 364 from a supply tank 366 containingthe liquid coolant. The pump 362 pumps liquid coolant through a feedline 367 to a filter 368 and therethrough to a radiator 369. From theradiator 369, the liquid coolant flows through a feed line 370 to themanifolds 96 and 98. These manifolds supply the high volume of liquidcoolant at low pressure to the dispensers 24 and 26 and to thedispensing manifolds 86 and 88 of one or more modules 100. For example,the liquid coolant may be provided in the range of 3 to 10 gal/min for a100 HP engine. As seen in FIG. 9C, a thermal valve 372 is connected inparallel with the radiator 369 between the output of the filter 368 andthe feed line 370. The state of the thermal valve 372 is controlled bythe temperature of the liquid coolant or by an emergency circuit 373.The emergency circuit 373 is also connected to the source valve 359. Alevel valve 375 has an input connected in common with the output of thefilter 368, the input of the radiator 369, and the input of the thermalvalve 372. The output of the level valve 375 is connected through a feedline 377 to the supply tank 366. The control linkage 361 is alsoconnected to control the state of the level valve 375.

With further reference to FIG. 9C, in normal operation, the level sensor360 detects the level of liquid coolant in the sump region 357 andselects as a source for the pump 362 either the sump region 357 or thesupply tank 366. When the operating level has been reached, the levelsensor sets the control linkage 361 to place the source valve in thestate where it draws liquid coolant only from the sump region 357. Theheated liquid coolant is pumped by the pump 362 through the filter 368to the radiator 369 and the thermal valve 372. When a design operatingtemperature of the liquid coolant is achieved, the thermal valve willclose partially or fully to modulate the flow of liquid coolant throughthe radiator 369, thereby regulating the engine temperature. The flow ofliquid coolant continues through the feed line 370 to the dispenserswhere the liquid coolant is applied to remove heat from the enginecomponents. If the level of liquid coolant in the sump region becomestoo high, the level sensor 360 causes the control linkage 361 topartially open the level valve 375 to return a portion of the liquidcoolant to the supply tank 366 after filtration at 368. In an emergencysituation where it is necessary to temporarily bypass the radiator 369,the emergency circuit 373 fully opens the thermal valve 372, therebyshunting the radiator 369, and forces the source valve 359 to initiallydraw liquid coolant from the supply tank 366. The excess liquid coolantthat accumulates in the sump region 357 will be removed by the levelvalve in response to the level sensor 360. For temporary maximumperformance, the thermal valve 372 is closed, thereby utilizing the fullcapacity of the radiator 369, while the state of the source valve 359 isset to draw fluid only from the supply tank 366.

A system 500 for providing charge air to and discharging exhaust gassesfrom an opposed-piston engine is illustrated in FIG. 10. The system mayscale to serve one or more cylinders 10. In the system 500, an air inletmanifold line 534 and an exhaust outlet manifold line 532 arerespectively connected to the inlet port tubes 84 and the exhaust porttubes 82 of one or more modules. These manifold lines are preferablymounted outside the engine enclosure. The engine schematicallyillustrated in FIG. 10 is a turbo-supercharged or supercharged engine.Thus, the manifold lines are connected to a turbo-supercharger 536.Specifically, the exhaust gases moving through the exhaust manifold line532 drive a turbine 540 en route to an output line 538 to mechanicallydrive a compressor 542. The compressor 542 draws air in on an air inletline 537 and pressurizes the intake air before directing air to theinlet manifold line 534 by way of an intercooler 539.

Other engine elements not included in the illustrations will be providedaccording to specific circumstances of each application of thisopposed-piston engine. In this regard, the gearbox 170 may be sealed andself-lubricated by oil or may be lubricated separately from the rest ofthe engine. Alternately, it could be left open and lubricated by thecoolant/lubricant used to cool and lubricate the pistons, provided thata suitable lubricant is employed.

In prior engines, as the BMEP increases, friction at the pistonring/cylinder interface increases and the interface temperature rises.The increasing interface temperature ultimately results in heat flowingback into the piston from the interface rather than from the piston tothe interface. As a consequence, the rings no longer cool the piston.Assuming maximum flow of coolant to the inside surfaces of the pistonskirt and crown, the only remaining piston surfaces to cool are theexterior surfaces of the skirt and crown. The exterior surface of thecrown is a component of the combustion chamber and is only marginallycooled by combustion gas expansion and scavenging airflow; this surfaceis otherwise inaccessible to external cooling. In prior art engines, theexterior surface of the piston skirt is also inaccessible to pistoncooling because the piston is encased in the cylinder. However, withperiodic exposure of the external surface of the piston skirt bysubstantially withdrawing the piston from the cylinder bore, thatsurface is available for cooling. As a result, on the order of twice theamount of heat transfer is achievable when compared with cooling onlythe inside surfaces of the piston skirt and crown. Enhanced engineperformance is thereby realized, with the result that opposed-pistonengines constructed according to this specification are capable ofachieving improved BMEP, specific output, and PWR when compared withprior art opposed-piston engines. For example an opposed-piston engineconstructed according to this specification will tolerate BMEP of atleast 200 psi, at least 250 psi, or at least 300 psi due to improvedcooling. Such an opposed-piston engine is capable of providing specificpower densities (SPD) of at least 11.0 HP/in², at least 12.0 HP/in², orat least 13.0 HP/in². These improvements enable this opposed-pistonengine to achieve a PWR of at least 0.5 HP/lb., at least 0.667 HP/lb, orat least 1.0 HP/lb.

The uses and applications of this opposed-piston engine are manifold. Itcan be scaled for any application using two-cycle engines, includingtwo-cycle diesel engines. The engine can be installed in or mounted on avariety of powered vehicles, tools, devices, or other apparatusrequiring the delivery of rotary power. See FIGS. 11A-11D for examplesin this regard. In FIG. 11A, this two-cycle opposed-piston engine 1100is installed in a surface vehicle, which can include wheeled or trackedvehicles, such as automobiles, motorcycles, scooters, trucks, tanks,armored military vehicles, snow-mobiles, and all equivalent and similarinstances. In FIG. 11B, this engine is installed in a water-goingvehicle such as a boat, hovercraft, submarine, personal water craft, andall equivalent and similar vehicles. In FIG. 11C, this engine isinstalled in a fixed or rotary-wing aircraft. In FIG. 11D, this engineis installed in a powered implement such as a lawnmower, edger, trimmer,leaf blower, snow blower, chain saw, and all equivalent and similardevices. In FIG. 11E, this engine is installed in an electrical powergenerating device. In FIG. 11F, the engine is installed in a pumpingdevice.

Although the invention has been described with reference to specificillustrations and examples, it should be understood that variousmodifications can be made without departing from the spirit of theprinciples of our engine. Accordingly, the invention is limited only bythe following claims.

1. An internal combustion engine, comprising: a frame including twobulkheads and beams attached to the bulkheads; at least one cylinderdisposed between the bulkheads; a pair of opposed pistons in the atleast one cylinder; each bulkhead including an I-beam section; a pair ofside-mounted crankshafts supported by the I-beam sections for rotation;a plurality of rods linking each piston to both crankshafts and adaptedto move in response to primarily tensile forces acting between thepistons and the crankshafts; the engine characterized by an engine cyclein which each piston is substantially withdrawn from the cylinder andthen driven back into the cylinder; and a system to apply a liquidcoolant to the external surface of each piston that is withdrawn fromthe at least one cylinder; wherein the crankshafts are adapted to rotatein opposite directions, the engine further including: a first gear onthe first crankshaft; a second gear on the second crankshaft; and, athird gear supported on the frame, the third gear having an annulus withan outside circumference engaging the first gear at a first location andan inside circumference engaging the second gear at a second locationopposite the first location.
 2. A combination for an internal combustionengine, including: a radially symmetric cylinder, including: a tube withtwo ends; a first manifold mounted to the tube at a first end; a secondmanifold mounted to the tube at a second end; an exhaust port in thefirst manifold; an inlet port in the second manifold; and, a fuelinjection element mounted to the tube; a pair of opposed pistonsdisposed in the cylinder and adapted to be at least partially withdrawnfrom the cylinder to receive externally-applied liquid coolant duringengine operation; and a dispenser apparatus for showering the liquidcoolant onto the outside surface of an external portion of each pistonwithdrawn from the cylinder.
 3. The combination of claim 2, the exhaustport including an annular gallery in the first manifold and the inletport including an annular gallery in the second manifold.
 4. Thecombination of claim 3, wherein each gallery comprises a continuousannular opening.
 5. The combination of claim 3, wherein each galleryincludes one or more bridges.
 6. The combination of claim 5, wherein thepistons are ringless.
 7. The combination of claim 5, further includingat least one ring mounted to each piston.
 8. A method for operating aninternal combustion engine including at least one cylinder with at leasttwo ports and a pair of opposed pistons disposed therein, including:causing the pistons to be at least partially withdrawn from the at leastone cylinder during engine operation; and showering an external surfaceportion of the skirt of each piston with a liquid coolant when theexternal surface portion is outside the cylinder.
 9. The method of claim8, further including applying the liquid coolant to an internal surfaceportion of each piston during engine operation.
 10. The method of claim9, further including applying the liquid coolant to the external surfaceof the cylinder.
 11. The method of claim 10, wherein the liquid coolantcomprises a fuel.
 12. The method of claim 11, wherein the engine is adiesel engine and the fuel is diesel fuel.
 13. A two-cycle, opposedpiston, internal combustion engine, comprising: at least one cylindermodule, wherein the at least one cylinder module is not in an engineblock; a pair of opposed pistons in each cylinder module and adapted tobe substantially withdrawn from the at least one cylinder module duringengine operation; each piston including a skirt and a crown; each pairof pistons adapted to be coupled to the engine so as to exert no sideforce on a cylinder module during engine operation; and means forshowering a liquid coolant onto an external portion of each piston thatis substantially withdrawn from a cylinder module; the cylinder modulecomprising: a tube with two open ends, a longitudinal center, and anoutside surface; a first manifold mounted to a first end of the tube; apiston-modulated exhaust port in the first manifold; a second manifoldmounted to a second end of the tube; a piston-modulated inlet port inthe second manifold; and a fuel injection element mounted to the tubenear the longitudinal center.
 14. The engine of claim 13, furtherincluding dispensers positioned to apply the liquid coolant to theoutside surface of the tube.
 15. The engine of claim 13, the meansincluding dispenser positioned to shower the liquid coolant ontoexternal surfaces of the skirts of the pistons outside of the cylindermodule.
 16. The engine of claim 15, further including dispenserspositioned to apply the liquid coolant to inside surfaces of the crowns.17. The engine of claim 14, further comprising: a pair of side-mountedcrankshafts; and a least three rods linking each piston to thecrankshafts to move the piston in response to substantially tensileforces between the piston and the respective crankshaft without exertingside force on a cylinder module.
 18. The engine of claim 16, furthercomprising a frame to support the pair of crankshafts for rotation. 19.The engine of claim 18, wherein the crankshafts are adapted to rotate inopposite directions, the engine further including: a first gear on thefirst crankshaft; a second gear on the second crankshaft; and, a thirdgear supported on the frame, the third gear having an annulus with anoutside circumference engaging the first gear at a first location and aninside circumference engaging the second gear at a second locationopposite the first location.
 20. An internal combustion engine,including: a frame including two bulkheads and beams attached to thebulkheads; a cylinder disposed between the bulkheads; a pair of opposedringless pistons in the cylinder; first and second side-mountedcrankshafts supported for rotation on beam sections of the bulkheads andhaving axes in a common plane normal to the axis of the cylinder; and,rods connecting each piston to the first crankshaft and to the secondcrankshaft.
 21. An internal combustion engine, comprising: a cylinderwith an internal bore; first and second opposed pistons adapted toreciprocate in the bore and to protrude from the bore during at least aportion of an operating cycle of the engine; first and second sidemounted crankshafts; connectors connecting the pistons to thecrankshafts; roller bearings supporting the crankshafts and couplingpoints of the connectors to the pistons and the crankshafts; and asupply system adapted to apply a liquid to the bearings to lubricate thebearings and to shower the liquid onto an external portion of eachpiston that protrudes from the bore to cool the piston.
 22. The internalcombustion engine of claim 21, wherein the engine is a compressionignition engine and the liquid is diesel fuel.